Saving ion-damaged spacers

ABSTRACT

Methods of selectively removing silicon oxide are described. Exposed portions of silicon oxide and spacer material may both be present on a patterned substrate. The silicon oxide may be a native oxide formed on silicon by exposure to atmosphere. The exposed portion of spacer material may have been etched back using reactive ion etching (RIE). A portion of the exposed spacer material may have residual damage from the reactive ion etching. A self-assembled monolayer (SAM) is selectively deposited over the damaged portion of spacer material but not on the exposed silicon oxide or undamaged portions of spacer material. A subsequent gas-phase etch may then be used to selectively remove silicon oxide but not the damaged portion of the spacer material because the SAM has been found to not only preferentially adsorb on the damaged spacer but also to halt the etch rate.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/404,143, filed Oct. 4, 2016 entitled “SAVING ION-DAMAGED SPACERS”. The disclosure of 62/404,143 is hereby incorporated by reference in its entirety for all purposes.

FIELD

Embodiments described herein relate to selectively removing material.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which removes one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.

Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors. For example, remote plasma excitation of ammonia and nitrogen trifluoride enables silicon oxide to be selectively removed from a patterned substrate when the plasma effluents are flowed into the substrate processing region. However, these processes have been found to undesirably move other exposed materials in addition to removing the target silicon oxide.

Methods are needed to improve silicon oxide etch selectivity relative to dissimilar materials for dry etch processes.

SUMMARY

Methods of selectively removing silicon oxide are described. Exposed portions of silicon oxide and spacer material may both be present on a patterned substrate. The silicon oxide may be a native oxide formed on silicon by exposure to atmosphere. The exposed portion of spacer material may have been etched back using reactive ion etching (RIE). A portion of the exposed spacer material may have residual damage from the reactive ion etching. A self-assembled monolayer (SAM) is selectively deposited over the damaged portion of spacer material but not on the exposed silicon oxide or undamaged portions of spacer material. Molecules of the self-assembled monolayer include a head moiety and a tail moiety, the head moiety forming a bond with the damaged portion of the exposed spacer material and the tail moiety extending away from the patterned substrate. A subsequent gas-phase etch using remotely excited combination of a hydrogen-containing precursor and a fluorine-containing precursor may then be used to selectively remove silicon oxide but not the damaged portion of the spacer material because the SAM has been found to halt the etch rate.

Methods described herein include protecting a damaged spacer portion on a patterned substrate. The methods include forming a conformal layer on a patterned substrate. Forming the conformal layer forms vertical and horizontal portions of the conformal layer. The methods further include reactive-ion etching the conformal layer on the patterned substrate. The reactive-ion etching removes horizontal portions of the conformal layer while retaining a vertical spacer. Reactive-ion etching exposes underlying silicon and forms a damaged spacer portion of the vertical spacer leaving an undamaged spacer portion of the vertical spacer. The methods further include selectively forming a self-assembled monolayer on the damaged spacer portion.

Selectively forming the self-assembled monolayer on the damaged spacer portion may not form the self-assembled monolayer on the undamaged spacer portion of the vertical spacer. The conformal layer may be a low-k dielectric. The conformal layer may include silicon, oxygen and carbon. The conformal layer may include only silicon, oxygen and carbon. The methods may further include shining UV light on the self-assembled monolayer to increase etch resistance. The methods may further include heating the self-assembled monolayer to increase integrity by baking the patterned substrate. The methods may further include removing a thin native oxide from the exposed underlying silicon which had formed upon a prior exposure to atmosphere. Removing the thin native oxide may not remove the self-assembled monolayer.

Methods described herein include reactive-ion etching a conformal layer on a patterned substrate. The methods include providing a patterned substrate having exposed silicon and exposed silicon oxide. The exposed silicon oxide has vertical sidewalls and is disposed above the exposed silicon. The methods further include forming a conformal layer on the patterned substrate. Forming the conformal layer covers the exposed silicon and the exposed silicon oxide, forming vertical and horizontal portions of the conformal layer. The methods further include reactive-ion etching the patterned substrate. Reactive-ion etching the patterned substrate reexposes the exposed silicon, reexposes the exposed silicon oxide, and forms vertical spacers on the vertical sidewalls. The vertical sidewalls include a damaged spacer portion near the top. The methods further include exposing the patterned substrate to an alkylsilane precursor. The methods further include selectively forming a protective film on the damaged spacer portion. The methods further include forming a native oxide on the exposed silicon by exposing the patterned substrate to atmosphere. The methods further include removing the native oxide. The methods further include removing the protective film.

Removing the native oxide may not remove the protective film. Selectively forming the protective film may not cover undamaged portions of the vertical spacers. The protective film may be a self-assembled monolayer. Each molecule of the self-assembled monolayer includes a head moiety and a tail moiety. The head moiety forming a covalent bond with the damaged spacer portion and the tail moiety extending away from the patterned substrate. The alkylsilane may include carbon, silicon, oxygen and hydrogen. The alkylsilane may include only carbon, silicon, oxygen and hydrogen. The alkylsilane may further include a halogen. The alkylsilane may be one of C8-methoxysilane, C7-methoxysilane, C6-methoxysilane, C5-methoxysilane, C4-methoxysilane, C3-methoxysilane, C5-chlorosilane, C4-chlorosilane or C3-chlorosilane.

Methods described herein include selectively depositing a protective layer onto a patterned substrate. The methods include providing a patterned substrate having two neighboring vertical spacers. The two neighboring vertical spacers have damaged spacer portions at the top and undamaged spacer portions at the bottom. The damaged spacer portions were damaged by an ion flux. An exposed silicon portion is disposed between the two neighboring vertical spacers. The methods further include selectively forming a self-assembled monolayer on the damaged spacer portions. The methods further include placing the patterned substrate in a substrate processing region. The methods further include flowing a hydrogen-containing precursor and a fluorine-containing precursor into a remote plasma region separated from the substrate processing region by a showerhead. The methods further include forming plasma effluents by forming a remote plasma in the remote plasma region. The methods further include flowing the plasma effluents through the showerhead and into the substrate processing region. The methods further include forming solid residue by reacting the plasma effluents with a native oxide on the exposed silicon portion. The methods further include sublimating the solid residue. The methods further include removing the self-assembled monolayer.

To better understand the nature and advantages of the present invention, reference should be made to the following description and the accompanying figures. It is to be understood, however, that each of the figures is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the present invention.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosed technology may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1A is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 1B is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 1C is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 1D is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 1E is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 1F is a side view of a patterned substrate during a reactive ion etching process according to embodiments.

FIG. 2 shows a method of reactive ion etching according to embodiments.

FIG. 3 shows a method of reactive ion etching according to embodiments.

FIG. 4A is a side view of a patterned substrate following formation of a self-assembled monolayer according to embodiments.

FIG. 4B is a side view of a patterned substrate during formation of a self-assembled monolayer according to embodiments.

FIG. 5A shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 5B shows a schematic cross-sectional view of a portion of a substrate processing chamber according to embodiments.

FIG. 6 shows a schematic cross-sectional view of a portion of a substrate processing chamber according to embodiments.

FIG. 7 shows a top view of an exemplary substrate processing system according to embodiments.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods of selectively removing silicon oxide are described. Exposed portions of silicon oxide and spacer material may both be present on a patterned substrate. The silicon oxide may be a native oxide formed on silicon by exposure to atmosphere. The exposed portion of spacer material may have been etched back using reactive ion etching (RIE). A portion of the exposed spacer material may have residual damage from the reactive ion etching. A self-assembled monolayer (SAM) is selectively deposited over the damaged portion of spacer material but not on the exposed silicon oxide or undamaged portions of spacer material. Molecules of the self-assembled monolayer include a head moiety and a tail moiety, the head moiety forming a bond with the damaged portion of the exposed spacer material and the tail moiety extending away from the patterned substrate. A subsequent gas-phase etch using remotely excited combination of a hydrogen-containing precursor and a fluorine-containing precursor may then be used to selectively remove silicon oxide but not the damaged portion of the spacer material because the SAM has been found to halt the etch rate.

Reactive-ion etching is used to separate a conformal layer of spacer material into spacers on the sides of features with vertical walls. FIGS. 1A, 1B, 1C, 1D, 1E and 1F are side views of a patterned substrate during a reactive ion etching process according to embodiments. A conformal layer of spacer material 105 is formed over a stack of polysilicon 108, silicon nitride 109 and silicon oxide 110 as shown in FIG. 1A. The stack of materials is part of substrate 101. A layer of spacer material 105 is formed conformally over silicon oxide 110 features in a wide variety of semiconductor processing applications. Reactive-ion etching is used (process depicted in FIG. 1B) to remove portions of conformal layer of spacer material 105 to form spacer(s) 115 as shown in FIG. 1C. Reactive-ion etching is used because of the high anisotropy of the etching process. Ions are accelerated in a chosen direction and may be directed perpendicularly toward substrate 101. The directionality of reactive-ion etching enables portions of conformal layer of spacer material 105 on top and between neighboring silicon oxide 110 features. “Top” and “Up” will be used herein to describe portions/directions perpendicularly distal from the substrate plane and further away from the center of mass of the substrate in the perpendicular direction. “Vertical” will be used to describe items aligned in the “Up” direction towards the “Top”. Other similar terms may be used whose meanings will now be clear.

Reactive-ion etching can be a destructive process. For example, reactive-ion etching can damage a portion of spacers 115 while removing the horizontal portions. FIG. 1C shows spacers 115 each having a damaged spacer portion 120 near the top. Subsequent processing may involve removing silicon oxide (e.g. a native oxide on silicon substrate 101) prior to performing a silicon recess in embodiments. In this work, the damaged spacer portion 120 has been found to wear down during removal of the native oxide as a consequence of the damage sustained during reactive-ion etching. The wearing down of damaged spacer portion 120 results in eroded damaged spacer portion 121 in FIG. 1F. Spacer 115 is defined herein as including damaged spacer portion 120 and the undamaged portion will refer to the portion of spacer 115 other than damaged spacer portion 120. Retaining even the damaged spacer portion 120 is desirable and is a benefit of the processes described herein. Recessed substrate 102 is shown in FIG. 1F after the native oxide is removed and the substrate is etched in the absence of a self-assembled monolayer (SAM).

A benefit of processes described herein involves retention of the damaged spacer portion 120 even after silicon oxide (e.g. native oxide on silicon) is removed for silicon recess in embodiments. Self-assembled monolayers 125, as described herein, have been found to adsorb preferentially on damaged spacer portions 120 rather than on exposed silicon oxide 110, undamaged spacer portions (the bottom portion of spacers 115) or exposed silicon 101 (as shown in FIG. 1D. An etchant is then introduced into a substrate processing region with the substrate to selectively remove silicon oxide. The silicon oxide may be in the form of a native oxide on substrate 101 prior to a silicon recess operation. Recessed substrate 102 is shown in FIG. 1E after etching the substrate. More of damaged spacer portion 120 remains in FIG. 1E than eroded damaged spacer portion 121 in FIG. 1F as a consequence of the intervening presence of the self-assembled monolayer 125.

To better understand and appreciate the embodiments, reference is now made to FIG. 2 which is a flow chart of a reactive-ion etch process 201 according to embodiments. A structure is formed in a patterned substrate (operation 210) which includes a silicon oxide portion having vertical sidewalls and a conformal spacer layer (a conformal layer of spacer material) formed thereon. Only the conformal spacer layer is exposed at this point in the process. The patterned substrate is etched in a directional ion etch which may be referred to herein as a reactive-ion etch (operation 220). The reactive-ion etch removes horizontal portions of the conformal spacer layer and retains the vertical portions. The vertical portions which remain are called spacers. The bottom portion of the spacers sustains considerably fewer collisions with ions from the anisotropic etching of the reactive-ion etch. The top portion bears the brunt of the damage from the ions of the reactive-ion etch. As a consequence, the top portion will be referred to as the damaged spacer portion, the bottom portion will be referred to as the undamaged spacer portion and the top and the bottom portions will be collectively referred to as the spacer.

A self-assembled monolayer (SAM) is formed on the patterned substrate by exposing the patterned substrate to a SAM precursor as described herein. The self-assembled monolayer has been found to preferentially form only on the damaged spacer portion (operation 230). Native oxide, exposed silicon oxide, exposed silicon and exposed silicon nitride appear to sustain much less or no deposition according to embodiments. In optional operation 240, the native oxide which develops on the exposed silicon of the substrate is removed. Removing the native oxide significantly eroded the damaged spacer portion in conventional processes but has been found to not etch or etch very slowly when the self-assembled monolayer is present. The process of removing the native oxide (operation 240) may be used to remove the self-assembled monolayer as well or an optional operation may be employed to remove the SAM layer or remnants thereof (operation 250).

FIG. 3 is also a flow chart of a reactive-ion etch process 301 according to embodiments. A structure is formed in a patterned substrate (operation 310) which includes a silicon oxide portion having vertical sidewalls. A layer of silicon nitride and/or a layer of polysilicon may lie under the silicon oxide in embodiments as described in FIGS. 1A-1F. A conformal spacer layer is formed on the silicon oxide and has horizontal portions on top of the silicon oxide and between neighboring silicon oxide features (operation 320). The conformal spacer layer also has vertical portions on the sides of the silicon oxide features which will become spacers in the ensuing operations. Only the conformal spacer layer is exposed at this point. The patterned substrate is reactive-ion etched in operation 330. The reactive-ion etch removes horizontal portions of the conformal spacer layer and retains the vertical portions. The vertical portions which remain are spacers. The bottom portion of the spacers sustains less damage from the reactive-ion etch and is again referred to as the undamaged spacer portion. The top portion sustains many more collisions from the accelerated ions and is referred to as the damaged spacer portion. The spacer may comprise or consist of the undamaged spacer portion and the damaged spacer portion according to embodiments. A self-assembled monolayer (SAM) is preferentially formed on the patterned substrate by exposing the patterned substrate to a SAM precursor. The self-assembled monolayer preferentially forms on the damaged spacer portion in operation 340.

The patterned substrate may be placed in a substrate processing region separated from a remote plasma region by a showerhead. A hydrogen-containing precursor (e.g. NH₃) and a fluorine-containing precursor (e.g. NF₃) are flowed into the remote plasma region and a remote plasma is formed (operation 350). Plasma effluents are formed in the remote plasma, flow through the showerhead and into the substrate processing region. The plasma effluents react with the patterned substrate to form solid residue from a reaction with native silicon oxide on an exposed surface of silicon (operation 360). The substrate processing region may be referred to as a plasma-free substrate processing region during any or all operations described herein aside from the reactive ion etch itself. Native oxide, exposed silicon oxide, exposed silicon and exposed silicon nitride appear to sustain much less or no deposition according to embodiments. The native oxide which develops on the exposed silicon of the substrate is desorbed or becomes solid residue in operation 360. The solid residue is sublimated by heating the patterned substrate in operation 370. Removing the native oxide does not etch or only etches the damaged spacer portion very slowly as a result of the presence of the self-assembled monolayer. Operation 360 and/or 370 have been found to beneficially remove the self-assembled monolayer as well in embodiments. As a consequence, removing the SAM layer (operation 380) may be optional as before.

According to embodiments, the self-assembled monolayer may be illuminated by and treated with UV-light to increase the longevity of the self-assembled monolayer during the etching of the silicon oxide. The UV-light may be from a H⁺-mercury lamp and the UV-light may comprise wavelengths between 200 nm and 400 nm in embodiments. Alone or in combination with the UV treatment, the self-assembled monolayer may be baked at elevated temperature to increase its resilience to the silicon oxide etch according to embodiments. The self-assembled monolayer may be baked by elevating the substrate temperature to between 200° C. and 450° C. or between 250° C. and 400° C. in embodiments. The duration of exposure to UV-light may be between 1 minute and 10 minutes according to embodiments. The duration of baking may be between 1 minute and 10 minutes in embodiments.

FIGS. 4A and 4B are side views of a patterned substrate following formation of a self-assembled monolayer according to embodiments. Undamaged spacer portion 415 and damaged spacer portion 420 are shown in each figure. FIG. 4A represents a close-up of FIG. 1D. Silicon oxide 410 is shown as well as the self-assembled monolayer 425. Self-assembled monolayers may be very sensitive to surface conditions or surface chemistry. FIG. 4A shows self-assembled monolayer 425 growing on a roughened surface which has been affected by the accelerated ions of reactive-ion etching. The cause of the high adsorption may relate to surface roughness or may relate to a chemical termination as indicated in FIG. 4B. A SAM precursor (N-propyltrimethoxylsilane) is shown in the gas phase above the surface. N-propyltrimethoxylsilane may preferentially react at hydroxyl (—OH) terminated surface sites to form the adsorbed SAM molecule 525 on the right of FIG. 4B.

The self-assembled monolayers described herein may be formed selectively over the damaged spacer portion by exposing the patterned substrate to an alkylsilane having a head moiety and a tail moiety. The alkylsilane may comprise or consist of carbon, silicon, oxygen and hydrogen in embodiments. The alkylsilane may further comprise a halogen. The alkylsilane may be one of C8-methoxysilane, C7-methoxysilane, C6-methoxysilane, C5-methoxysilane, C4-methoxysilane, C3-methoxysilane, C5-chlorosilane, C4-chlorosilane or C3-chlorosilane according to embodiments. The tail moiety may function to prevent or discourage etching of damaged spacer portions. The tail moiety of the SAM molecule (the alkylsilane) may include an alkyl group having more than 2 carbon atoms, more than 3 carbon atoms, more than 4 carbon atoms, more than 5 carbon atoms, or more than 6 carbon atoms, covalently bonded in a chain in embodiments. Depending in part on the length of the tail moiety, the deposition precursor may be in gas, liquid or solid form which may be provided to the patterned substrate with a variety of appropriate techniques. Gas precursors may be delivered to a chemical vapor deposition chamber as in the second example. Liquids and solids may be vaporized and carried into a chemical vapor deposition chamber using a relatively inert carrier gas in embodiments. Alternative hardware for delivering liquid deposition precursors to the patterned substrate will also be provided herein. The patterned substrate may be exposed to an alkylsilane in the liquid or gas phase. Exemplary hardware used for depositing self-assembled monolayers using a liquid precursor will be described shortly.

The deposition precursors used to deposit the self-assembled monolayers herein may be described as SAM molecules especially when tail moieties (TM) and head moieties (HM) and minute interactions between the precursors and the patterned substrate are being described. Generally speaking, the tail moiety may be a linear or branched alkyl chain or may be a cyclic hydrocarbon in embodiments. The tail moiety may comprise or consist of carbon and hydrogen according to embodiments. Regardless of shape, the tail moiety may be a fluorinated hydrocarbon and may comprise or consist of carbon, hydrogen and fluorine in embodiments. The head moiety may be a methoxysilane (e.g. a dimethoxysilane or a trimethoxysilane), an ethoxysilane (e.g. a diethoxysilane or a triethoxysilane), an amine silane, an amino silane, a silazane or a chlorosilane. The SAM precursor may have a tail which is a fluorinated alkylsilane in embodiments. The SAM molecules may be one or more of n-propyltrimethoxysilane, n-octyltrimethoxysilane, or trimethoxy(octadecyl)silane according to embodiments. The SAM precursor may have a tail which is a phenyl group and may be a phenyl alkylsilane in embodiments.

The hydrogen-containing precursor may comprise one or more of H₂ or H₂O in embodiments. The fluorine-containing precursor may include one or more of F₂, NF₃ or FCl₃ according to embodiments.

Exposed silicon, exposed silicon nitride, undamaged spacer portion and exposed silicon oxide may not be chemically modified by the same chemical preparation which affects the damaged spacer portion. All but the damaged spacer portion may therefore not develop hydroxyl termination and may not react with the SAM molecules of the alkylsilane precursor. The SAM is formed from the alkylsilane precursor by the chemisorption of the head moiety onto a substrate from either the vapor or liquid phase followed by a general alignment of tail moiety distal from damaged spacer portion bonding sites. The tail moiety may not chemically bond to either silicon, silicon oxide, spacers, or silicon nitride according to embodiments. Once all silicon oxide bonding sites on exposed silicon oxide portion are occupied with adsorbed alkylsilane, the bonding process may cease, becoming a self-limiting process. The spacers and the conformal spacer layers described herein may be a low-k dielectric. The conformal spacer layer may comprise or consist of silicon, oxygen and carbon in embodiments.

The self-assembled monolayers may be thermally stable and can withstand thermal processing at relatively high temperatures up to 400° C., up to 450° C. or even up to 500° C. A temperature of the patterned substrate is less than 400° C., less than 450° C. or less than 500° C. during the operation of forming the self-assembled monolayer according to embodiments.

Exemplary hardware will now be described. FIGS. 5A and 5B are schematic views of substrate processing equipment according to embodiments. FIG. 5A shows hardware used to expose substrate 1105 to a liquid deposition precursor solution 1115-1 in a tank 1101. Substrate 1105 may be lowered into solution 1115-1 using a robot and may be supported by substrate supports 1110 during processing. FIG. 5B shows alternative hardware which spins substrate 1105 while pouring liquid deposition precursor solution 1115-2 from a dispenser 1120 across the top surface of the substrate.

FIG. 6 is a partial cross sectional view showing an exemplary substrate processing chamber 1201 which may be used to perform portions of processes described herein. A hydrogen-containing precursor and a fluorine-containing precursor may be introduced through one or more apertures 1251 into remote plasma region 1265. The precursors may or may not be excited by plasma power source 1246 in embodiments. Substrate processing chamber 1201 includes chamber body 1212 and substrate pedestal 1210. The substrate pedestal 1210 is at least partially disposed within the chamber body 1212. Substrate processing chamber 1201 may include a vacuum pump 1225 and a throttle valve 1227 to regulate flow of gases through the processing chamber 1201 and substrate processing region 1240 therein. The vacuum pump 1225 is coupled through the chamber body 1212 and in fluid communication with the interior of substrate processing chamber 1201.

Substrate processing chamber 1201 includes electrode 1245 to generate a plasma of reactive species in remote plasma region 1265. Electrode 1245 is supported by top plate 1250 and is electrically isolated therefrom by electrically isolating ring(s) 1247 made from aluminum oxide or any other insulating and process compatible material in embodiments. Electrode 1245 is coupled to a power source 1246 while showerhead 1220 is connected to ground (e.g. through showerhead flange 1222). Power source 1246 may be an RF power supply. A plasma of precursors (e.g. a hydrogen-containing precursor and a fluorine-containing precursor) can be generated in remote plasma region 1265 between electrode 1245 and showerhead 1220. In embodiments, the plasma can be struck and contained between the electrode 1245 and showerhead 1220 in remote plasma region 1265. Accordingly, the plasma is a “remote plasma” since no active plasma is in direct contact with substrate 1211 disposed within the chamber body 1212. As a result, plasma damage to substrate 1211 may be avoided since the plasma is separated from the substrate surface.

The substrate temperature may be controlled by applying heat to or cooling substrate pedestal 1210. In embodiments, showerhead 1220 may be maintained at a temperature higher than the substrate and the substrate can be physically elevated to raise the substrate temperature above the sublimation point of solid residue by-products. In this case the substrate is heated radiatively or by using a gas to conduct heat from showerhead 1220 to the substrate. The substrate may be elevated by raising substrate pedestal 1210 or by employing lift pins to raise substrate 1211 relative to substrate pedestal 1210.

Plasma effluents may include NH₄F and NH₄F.HF which react readily with low temperature substrates described herein. The substrate temperature may be below 50° C., below 60° C., below 70° C. or below 80° C. during exposure to the plasma effluents. Plasma effluents may react with a silicon oxide surface to form (NH₄)₂SiF₆, NH₃ and H₂O products. The NH₃ and H₂O are vapors under the processing conditions described herein and may be removed from substrate processing region 1240 by vacuum pump 1225 during the exposure. A thin continuous or discontinuous layer of (NH₄)₂SiF₆ solid by-products may be left behind on the substrate surface. Following exposure to plasma effluents and the associated accumulation of solid by-products, the substrate may be heated to remove the by-products. In embodiments, the showerhead 1220 is heated using an embedded heating element within or near showerhead 1220. The substrate may be heated by reducing the distance between the substrate and the heated showerhead. Showerhead 1220 may be heated to between 100° C. and 150° C. according to embodiments. By reducing the separation between the substrate and the heated showerhead 1220, the substrate may be heated to above 85° C., above 90° C., above 100° C. or between 110° C. and 150° C. in embodiments. The heat radiated from showerhead 1220 to the substrate should be made sufficient to dissociate or sublimate solid (NH₄)₂SiF₆ on substrate 1211 into volatile SiF₄, NH₃ and HF products which may be pumped away from substrate processing region 1240. Other methods of imparting heat to substrate 1211 may also be used.

Nitrogen trifluoride (or another fluorine-containing precursor) may be flowed into remote plasma region 1265 at flowrates between 25 sccm and 200 sccm according to embodiments. Ammonia (or hydrogen-containing precursors in general) may be flowed into remote plasma region 1265 at flowrates between 50 sccm and 300 sccm in disclosed embodiments. Production of plasma effluents occurs within remote plasma region 1265 by applying plasma power to electrode 1245 relative to showerhead 1220. Plasma power can be a variety of frequencies or a combination of multiple frequencies. In embodiments, the plasma is provided by RF power delivered to electrode 1245. The RF power may be between about 1 watt and about 1000 watts, between about 5 watts and about 600 watts, between about 10 watts and about 300 watts or between about 20 watts and about 100 watts according to embodiments. The RF frequency applied in the exemplary processing system may be less than about 200 kHz, less than about 150 kHz, less than about 120 kHz or between about 50 kHz and about 90 kHz in embodiments. The pressure in substrate processing region 1240 (and in remote plasma region 1265) may be maintained between 0.5 Torr and 1,000 Torr or between 20 Torr and 110 Torr during the flow of plasma effluents according to embodiments.

Embodiments of the systems described herein may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 7 shows one such processing system (mainframe) 2101 of deposition, etching, baking, and curing chambers in embodiments. In the figure, a pair of front opening unified pods (load lock chambers 2102) supply substrates of a variety of sizes that are received by robotic arms 2104 and placed into a low pressure holding area 2106 before being placed into one of the substrate processing chambers 2108 a-f. A second robotic arm 2110 may be used to transport the substrate wafers from the holding area 2106 to the substrate processing chambers 2108 a-f and back. Each substrate processing chamber 2108 a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes.

The term “gap” is used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, gaps may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A “trench” is a long gap. A trench may be in the shape of a moat around an island of material whose aspect ratio is the length or circumference of the moat divided by the width of the moat. The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interface likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.

As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂ but may include concentrations of other elemental constituents such as, e.g., nitrogen, hydrogen and carbon. In some embodiments, silicon oxide portions described herein consist of or consist essentially of silicon and oxygen. Exposed “silicon” or “Si” of the patterned substrate is predominantly silicon but may include concentrations of other elemental constituents such as, e.g., boron, phosphorus, oxygen, nitrogen, hydrogen and carbon. In some embodiments, silicon portions described herein consist of or consist essentially of silicon.

The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well-known processes and elements have not been described to avoid unnecessarily obscuring the present embodiments. Accordingly, the above description should not be taken as limiting the scope of the claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the claims, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

The invention claimed is:
 1. A method of protecting a damaged spacer portion on a patterned substrate, the method comprising: forming a conformal layer on a patterned substrate, wherein forming the conformal layer forms vertical and horizontal portions of the conformal layer; reactive-ion etching the conformal layer on the patterned substrate, wherein the reactive-ion etching removes horizontal portions of the conformal layer while retaining a vertical spacer; and wherein reactive-ion etching exposes underlying silicon and forms a damaged spacer portion of the vertical spacer leaving an undamaged spacer portion of the vertical spacer; and selectively forming a self-assembled monolayer on the damaged spacer portion.
 2. The method of claim 1 wherein selectively forming the self-assembled monolayer on the damaged spacer portion does not form the self-assembled monolayer on the undamaged spacer portion of the vertical spacer.
 3. The method of claim 1 wherein the conformal layer is a low-k dielectric.
 4. The method of claim 1 wherein the conformal layer comprises silicon, oxygen and carbon.
 5. The method of claim 1 wherein the conformal layer consists of silicon, oxygen and carbon.
 6. The method of claim 1 further comprising: shining UV light on the self-assembled monolayer.
 7. The method of claim 1 further comprising: heating the self-assembled monolayer to increase integrity by baking the patterned substrate.
 8. The method of claim 1 further comprising: removing a thin native oxide from the exposed underlying silicon which had formed upon a prior exposure to atmosphere, wherein removing the thin native oxide does not remove the self-assembled monolayer.
 9. A method of reactive-ion etching a conformal layer on a patterned substrate, the method comprising: providing a patterned substrate having exposed silicon and exposed silicon oxide, wherein the exposed silicon oxide has vertical sidewalls and is disposed above the exposed silicon; forming a conformal layer on the patterned substrate, wherein forming the conformal layer covers the exposed silicon and the exposed silicon oxide, forming vertical and horizontal portions of the conformal layer; reactive-ion etching the patterned substrate, wherein reactive-ion etching the patterned substrate reexposes the exposed silicon, reexposes the exposed silicon oxide, and forms vertical spacers on the vertical sidewalls, wherein the vertical sidewalls comprises a damaged spacer portion near the top; exposing the patterned substrate to an alkylsilane precursor; selectively forming a protective film on the damaged spacer portion; forming a native oxide on the exposed silicon by exposing the patterned substrate to atmosphere; and removing the native oxide.
 10. The method of claim 9 wherein removing the native oxide does not remove the protective film.
 11. The method of claim 9 wherein selectively forming the protective film does not cover undamaged portions of the vertical spacers.
 12. The method of claim 9 wherein the protective film is a self-assembled monolayer.
 13. The method of claim 12 wherein each molecule of the self-assembled monolayer includes a head moiety and a tail moiety, the head moiety forming a covalent bond with the damaged spacer portion and the tail moiety extending away from the patterned substrate.
 14. The method of claim 9 wherein the alkylsilane precursor comprises a cyclic hydrocarbon group.
 15. The method of claim 9 wherein the alkylsilane precursor comprises a linear or branched alkyl chain.
 16. The method of claim 9 wherein the alkylsilane precursor further comprises a halogen.
 17. The method of claim 9 wherein the alkylsilane precursor is one of C8-methoxysilane, C7-methoxysilane, C6-methoxysilane, C5-methoxysilane, C4-methoxysilane, C3-methoxysilane, C5-chlorosilane, C4-chlorosilane or C3-chlorosilane.
 18. A method of selectively depositing a protective layer onto a patterned substrate, the method comprising: providing a patterned substrate having two neighboring vertical spacers, wherein the two neighboring vertical spacers have damaged spacer portions at the top and undamaged spacer portions at the bottom, and wherein the damaged spacer portions were damaged by an ion flux, and wherein an exposed silicon portion is disposed between the two neighboring vertical spacers; selectively forming a self-assembled monolayer on the damaged spacer portions; placing the patterned substrate in a substrate processing region; flowing a hydrogen-containing precursor and a fluorine-containing precursor into a remote plasma region separated from the substrate processing region by a showerhead; forming plasma effluents by forming a remote plasma in the remote plasma region; flowing the plasma effluents through the showerhead and into the substrate processing region; forming solid residue by reacting the plasma effluents with a native oxide on the exposed silicon portion; and sublimating the solid residue. 